The present invention relates to a method for producing a cylinder block, and more particularly, to such a method including the steps of holding an inner peripheral surface of a cylinder liner by a metal mold, filling a molten metal around the cylinder liner, the molten metal being a material of the cylinder block body, and melt-bonding the molten metal to the cylinder liner.
An insert is conventionally performed for producing a cylinder block in which a molten metal which is a material of the cylinder block body is filled around the cylinder liner. Laid-open Japanese Patent Application publication No. Hei-10-94867 discloses a method for producing a cylinder block. The method includes the steps of performing a shot blast to the outer peripheral surface of the cylinder liner, and then setting the cylinder liner at a predetermined position of a metal mold for casting a cylinder block body. According to this method, particles used in the shot blast are of fragment forms, tetrahedron forms, pyramid forms or lancet forms those having acute angles, and these particles are blown onto the outer peripheral surface of the cylinder liner. Average particle size is about 70 xcexcm. Connection between the cylinder liner and the block body can be ensured by roughening the outer peripheral surface of the cylinder liner upon impingement of the particles thereonto.
However, in the conventional method for producing the cylinder block, optimum integral condition for the connection between the cylinder liner and the cylinder block body is unclear such as a condition of shot blast capable of providing efficient heat transmission from the cylinder block body to the cylinder liner when connecting the block body and the cylinder liner together. Further, average particle size in the conventional shot blast is 70 xcexcm. However, no theoretical support is provided as to this particle size. Furthermore, in the conventional shot blasting method, spherical particles are not used but fragmental particles having acute angle are used. Therefore, size of the spherical particles, if used in the shot blasting method, is not clear.
It is therefore, an object of the present invention to provide a method for producing a cylinder block, the method being capable of providing improved bonding between the cylinder block body and the cylinder liner.
This and other objects of the present invention will be attained by providing a method for producing a cylinder block including the steps of outer surface roughening process, melt bonding process and inner surface roughening process. In the outer surface roughening process, an outer peripheral surface of a cylinder liner formed of aluminum alloy is roughened by shot blasting. In the melt bonding process, a molten metal is melt bonded to the outer peripheral surface of the cylinder liner by filling the molten metal around the outer peripheral surface of the cylinder liner, while the cylinder liner is held to a metal mold by abutting the metal mold to an inner peripheral surface of the cylinder liner. In the inner surface roughening process, the inner peripheral surface of the cylinder liner is roughened by shot blasting prior to the melt-bonding step.
In this method, contacting degree between the cylinder liner and the metal mold can be lowered by the inner peripheral surface roughening process by means of shot blasting to the inner peripheral surface. Thus, heat insulation between the cylinder liner and the metal mold can be improved. Accordingly, temperature decrease of the cylinder liner can be restrained during melt bonding process, thereby improving melt bonding between the cylinder liner and the block body.
Preferably, the shot-blasting for roughening the outer peripheral surface includes the step of forming semi-spherical recesses at the outer peripheral surface by striking at least one shot ball onto the outer peripheral surface. Because semi-spherical dimples are formed at the outer peripheral surface of the cylinder liner by shot blasting the outer peripheral surface in the outer peripheral surface roughening process, heat transmission coefficient from the molten metal to the cylinder liner can be enhanced. Therefore, melt bonding degree between the molten metal as the block body and the cylinder liner can be enhanced.
Preferably, the method further includes the step of adhering adiabatic powders onto the inner peripheral surface of the cylinder liner after roughening the inner peripheral surface and prior to the melt bonding step. Because the adiabatic particle is adhered to the inner peripheral surface of the cylinder liner in the adhesion process, heat insulation between the metal mold and the cylinder liner can be enhanced thereby restraining temperature decrease of the cylinder liner during the melt bonding process. Thus, melt bonding between the cylinder liner and the block body can be improved.